Thermal Storage
To build up the bottom to where the slab could be poured, 60 tons of fill was needed. This would raise the bottom up about 1 ½ feet to be done in 4 lifts, or layers, with each layer being compacted and plastic water tubes set in stone dust. After discussing the application with the supplier and others in the business, the best product to use was a graded rock mix with a lot of fines, called State DOT Mix #5. This is the same stuff they use for roads and it cost $8 per ton. A tandem truckload carries about 20 tons of material and gives about 6" of depth for our job. The first tandem delivered on Saturday, August 21 but we couldn’t work because of the rain. I had to punch a hole in the bottom of the block foundation at the back to let out the water that collected in the pit. On Sunday, August 22 and Monday, August 23 night, we prepared the thermal storage container by lining the bottom and sides with 2" of rigid extruded polystyrene by Dow, sold under the trade name Foamular 250.
In the 2" thickness the best price that I could find was $1.20 per square foot. I used 2 layers of 1", the price was the same and it was a little easier to work with. The stuff wasn’t cheap but I know that having it will pay off in the long run. Al Romano helped me out. The insulation was set on the sides first. It was important that the top edge was straight because we would eventually use it as a form for the slab.
The mason’s crew loaded the first 20 tons in the bottom by hand. It took 4 men all day. It was a hard job. The following day they rented a vibratory plate compactor and compacted it flat.
Big rains were predicted for Saturday. I had another 20 tons of dust and 20 tons of mix #5 delivered. Since I couldn’t afford more rain delays, I bought a 40x60’ blue poly tarp to cover the foundation. I strung up a line between the house and a tree at the edge of the yard. The tarp went over the line and was tied off at the edges.
Luckily it only drizzled that day. It went in much faster this time because I had Al Romano help us with his bobcat.
At noon, I rented a walk behind vibrating roller compactor. This piece of equipment weighed 2,000 lbs. We had to build ramps to get it down into the pit.
On Sunday, 2 of the workers finished covering the third and last tubing circuit by hand.